" Adapt and survive, " goes the business-world cliché. For bands, at least those with integrity, it’s more a matter of evolution than adaptation. And Yo La Tengo have continued to evolve in interesting ways for 19 uninterrupted years, which may be a record in the realm of indie rock.

Launched by husband-and-wife team Ira Kaplan and Georgia Hubley on a kind of rocket fuel that blended smart pop songwriting with prickly noise-obsessed guitar, the band made recordings that worked through raw psychedelia to angular exploratory improvisations to pure folk music (1990’s excellent Bar/None release Fakebook) and back again; the journey culminated with the studio album of songs And Then Nothing Turned Itself Inside-Out (Matador), a critically heralded 2000 release that explored the dynamics of marriage. If there’s been a single musical obsession that’s sustained the group through the years, it’s their love for the unconventional rock instincts of the Velvet Underground. Although eschewing Lou Reed’s demi-monde in their lyrics, Yo La Tengo have taken a similar glee in incorporating everything from raga riffs, falling amplifiers, drum machines, and duct-taped organ keys into their sound. Today they remain a vital link to the VU’s ragged courageous spirit and sonics as well as the trimmer compositional instincts and angularity of the later punk era. It’s hard to image slow-rockers Tortoise and Boston’s jagged pop rebels Red Telephone without the torch passed by Yo La Tengo.

But the new Summer Sun (Matador) veers off in what sounds like a new direction. It isn’t really, as Kaplan points out over the phone: " Starting with [1993’s] Painful, we’ve been pretty interested in textural music. " Nonetheless, Summer Sun is startling compared with their other song-oriented albums. It’s the quietest one they’ve ever made, blending a Velvet-like penchant for repetition with spare, low-key instrumentation plied in the service of melodies plucked from the terrain of folk and lounge music. Also, the CD’s 13 pieces seem less spontaneous, and there are fewer of the epic guitar solos that have characterized Kaplan’s playing in recent years.

Kaplan admits the disc has Yo La Tengo’s most groove-oriented and most melodic composing, " though we didn’t calculatedly plan it that way. We made the record the same way we always do, which is to get together and play and see where things go from there. " He says that Summer Sun carries on the work that the trio, which is completed by bassist/keyboardist/guitarist James McNew, began with 2002’s The Sounds of the Sounds of Science (Matador). That disc, which largely slipped through the cracks, was a soundtrack to the undersea documentaries of French filmmaker Jean Painlevé. All its numbers are instrumental, and most clock in at eight to 10 minutes — a radical departure from And Then Nothing Turned Itself Inside-Out.

" We began making the music for the films as we had prepared to record songs in the past — writing songlike pieces, but without lyrics, " Kaplan says. " Then when we started playing the music along with the films, it wasn’t working. It needed to change shape. " Which meant the music had to lose some of its brash and bristly rock-and-roll qualities and relax. Rhythms became gentler and more ambling, less pushy. More melodies were needed to sustain the mood of the shadowy ocean world of the films. Although not as loud and fiery as their earlier work, the result was a broadening of Yo La Tengo’s sonic canvas — like switching from a conventional movie to widescreen Cinemascope.

So it goes with Summer Sun. Although most tunes run from two to five minutes, it’s too expansive to be a pop album. Sounds and moods rule, not songs. With shimmering vibrato guitars, violins, loops, keyboard washes, layers of cymbal spray, and percussive flourishes tucked into every cranny of the mix, and all played with subtlety and taste, the CD seems to borrow more from film composer Ennio Morricone, early Pink Floyd, and even French cabaret master Serge Gainsborough than from the Velvets or Yo La Tengo’s own history. And Kaplan and Hubley are singing differently. The hushed tones they bring to the gentle, carefully formed vocal melodies of numbers like " How To Make a Baby Elephant Float " and " Today Is the Day " blend into the other sounds. They’re not so much telling stories as aiming to sustain tranquil, sometimes playful, moods.

What this approach brings to Yo La Tengo’s game is that Cinemascopic quality. And as " Beach Party Tonight " and " Little Eyes " begin the album, it’s obvious that their palette is the richer for it. The keyboards and the droning guitars swirl out of the stereo speakers to provide a kind of sonic headrush that’s sustained all the way through. In that regard, it’s a stoner’s album — intoxicating with a shifting, drifting sonic terrain that seems as wide as Texas.

What was troubling about Yo La Tengo’s performance a week ago Wednesday at the Roxy is that the boldly writ music of Summer Sun didn’t seem to work live. Openers Portastatic were no help. They played a set of disjointed buzz pop that left much of the audience restless. The band, a side project of Superchunk’s Mac McCaughan, had a hard time locking together until the last few songs, and by then it was too late to capture the near-capacity crowd. True to their lo-fi nature, at least as defined by their albums, Portastatic began the night with a song that called for just acoustic guitar, melodica, and McCaughan’s voice. That was underwhelming in a large space like the Roxy. As Sebadoh’s Lou Barlow would readily admit, lo-fi outfits usually have trouble bringing their best to the stage.

Not so Yo La Tengo, who have always managed to float their bumpy pop constructions live on a kind of adrenal blast or by spinning out trance-inducing sonics, either via long, unpredictable guitar excursions or a blend of heartbeat rhythms and penetrating vintage organ notes. The songs on Summer Sun promised plenty of the latter, but at this gig vital energy seemed to be missing. It was as if they’d spent it all on the opening jam, when Kaplan slammed his guitar’s whammy bar and strode around the stage to find the sweetest spots for making his amps scream with feedback and Hubley and McNew gave him plenty of gas for the wild ride.

Large as the scope of even quiet numbers like " Nothing But You and Me " seems on Summer Sun, with explosions made by kicking the reverb boxes in their fender amps, multiple keyboard lines that slither around one another, the shimmer and patter of Hubley’s cymbal and brush work, and guitar riffs that float in a sea of echo, the music doesn’t work its magic in a large space. Without the enveloping quality that a good pair of headphones or stereo speakers can create, the textural depth of the songs was lost. Even " Today Is the Day, " which blends a slide-guitar line with a cocktail-lounge rhythm and a dreamy vocal to make an indelible impression on CD, didn’t reach the fans. Boston rock audiences are notorious for talking through performances, but just off the dance floor the chatter of a less-than-riveted crowd was loud enough to compete with the fully amplified band.

I should point out that Yo La Tengo were just a few days into the tour, and playing this material in front of audiences for the first time. " We’re kind of relearning how to do things on stage because the songs are so different, " Kaplan offers. " Really, it’s a shock to us how different it is. It’s hard to explain, but I know it’s more than just going back on tour after a long break. This is music we really have to approach in a way that we’re just discovering live. "

WHEN YO LA TENGO’S TOUR is finished, expect to see James McNew back in town to support A Grown-Ass Man (Shrimper), the new CD from his one-guy band Dump. It’ll be a homecoming of sorts, since McNew arrived as an indie-rock playah while a member of the Boston group Christmas, who dissolved when members Michael Cudahy and Liz Cox formed Combustible Edison and helped launch what turned into an insufferable lounge-rock trend.

Whereas Summer Sun’s songs sprawl across a broad canvas, McNew’s latest Dump is small and messy, a lo-fi bedroom recording along the lines of Sebadoh’s midlife albums. It sounds less like a four-track recording than do Dump’s previous releases — which include the Prince tribute That Skinny Motherfucker with the High Voice? (Shrimper) — but just marginally so, striking a balance between charm and laziness. There’s too much drum machine and not enough effort invested in some of the album’s vocal performances, like " Sisters, " a fractured love ballad driven by cheesy keyboard and a Wurlitzer-organ beatbox-like rhythm.

Dump does best when McNew opens up — whether he’s giving his guitar full hearty strums or simply singing as if he weren’t under the cloud of a life sentence of small-town ennui. In short, when he skips the slacker bullshit. The new Dump does best when it’s uptempo. The energy level of the buzzing " Basic Cable, " which is launched by a squiggle of hot amplifier feedback, seems to drive McNew to focus on crafting its melody line and harmonies — to keep things streamlined and efficient so the " don’t make me wait " refrain grabs your attention. Then there’s " Daily Affirmation, " where clouds of raw, distorted guitar billow like the smoke from an oil fire. The introspective lyrics evoke Neil Young as much as the raw slash of his chords and his staccato soloing. McNew steers clear of the high vocal register he uses on much of the album, sidestepping a total cop of Young’s style.

Now I don’t want to call McNew lazy (again), but the best lyrics and arrangements are covers that follow the original structures. The late Phil Lynott’s " Cowboy Song " starts with an acoustic intro before venting its macho arena-rock passions with big guitars and swaggering lyrics, providing McNew with fodder for a change in dynamics and a chance to indulge both the sweet and the raw sides of his voice. The most arresting number on A Grown-Ass Man is a cover of modern soul singer Gerald Levert’s " Mr. Too Damn Good, " which opens with a slow-but-strong wah-wah guitar solo that yields to the vocal melody, where McNew’s phrasing follows Levert’s roadmap. It’s a great little story of whole-hearted devotion. The chorus runs, " Wanna be the smile on your face/Be the stars in your moon/Wanna be your sunny day/Can I be your favorite tune?/I wanna be your breakfast in bed/Baby I’ll be your fool/Mr. Too Damn Good to you. " There’s no room for distance when you’re singing lines like that, and it shows in McNew’s delivery. Given his obvious affection for this music, it’s surprising he hasn’t allowed its spirit to trickle into his rock/pop numbers more. A little taste of soul goes a long way.